crystal structures and solid-state cpmas 13c nmr correlations in luminescent zinc(ii) and...

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Crystal structures and solid-state CPMAS 13C NMR correlations inluminescent zinc(II) and cadmium(II) mixed-ligand coordination polymersconstructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate†

Hesham A. Habib,a Anke Hoffmann,b Henning A. Hoppea and Christoph Janiak*a

Received 23rd July 2008, Accepted 3rd October 2008First published as an Advance Article on the web 16th January 2009DOI: 10.1039/b812670d

The hydrothermal reaction of M(NO3)2·4H2O (M = Zn and Cd) with benzene-1,4-dicarboxylicacid (H2bdc) or benzene-1,3-dicarboxylic acid (H2ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre)produced the mixed-ligand coordination polymers (MOFs) 3

•{[Zn2(m2-bdc)2(m4-btre)]} (1),3•{[Cd2(m4-bdc)(m4-btre)2](NO3)2·H2O} (2) and 2

•{[Zn2(m3-ip)2(m2-btre)(H2O)2]·2H2O} (3). Thecompounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-statecross-polarization (CP) magic-angle-spinning (MAS) 13C NMR and thermoanalysis, feature 3Dmetal–organic frameworks for 1 and 2 and 2D double layers which are connected through hydrogenbonds from the aqua ligands for 3. The CPMAS 13C NMR spectra picture the symmetry-independent(unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zincand cadmium coordination polymers 1–3 show a strong bluish fluorescence upon excitation with UVlight (the free btre ligand is non-luminescent).

Introduction

Metal–organic frameworks (MOFs) or coordination polymersattract much attention in recent years because of topology andpotential applications in catalysis, adsorption (gas storage), lumi-nescence, magnetism, etc.1–4 Luminescent stable metal–organic co-ordination polymers have been an active research area for decadesbecause of their potential applications in materials science.1,5,6

Mixed-ligand coordination polymers7,8 based on a luminescentand a non-luminescent ligand should allow for a dilution ofthe luminescent centers to avoid concentration quenching effects.Multi-carboxylate ligands with suitable spacers, especially benzoicacid-based ligands and also the 1,2,4-triazole ligand and itsderivatives9 are frequent choices for metal–organic networks.1

Benzenedi- or -tricarboxylates can exhibit luminescence in coor-dination polymers with metal nodes such as zinc or cadmium.5,10

Benzene-1,4-dicarboxylate,11 (bdc2-, terephthalate, Scheme 1) witha 180◦ angle between the two carboxylic groups, can form shortbridges via one carboxylato end, thereby simultaneously linkingup to four metal ions within a metal–metal separation of about11 A,12–15 or it forms long bridges via the benzene ring, leading toa great variety of structures.16,17 Also benzene-1,3-dicarboxylate,(ip2-, isophthalate)18 in which the two carboxylate moieties arerigidly predisposed at 120◦ (Scheme 1), is an equally good oxygen

aInstitut fur Anorganische und Analytische Chemie, Universitat Freiburg,Albertstr., 21, 79104, Freiburg, Germany. E-mail: [email protected];Fax: +49 761 2036147; Tel: +49 761 2036127bInstitut fur Makromolekulare Chemie, Universitat Freiburg, Stefan-Meier-Str. 31, D-79104, Freiburg, Germany. E-mail: [email protected]; Fax: +49 761 2036306; Tel: +49 761 2036314† Electronic supplementary information (ESI) available: X-Ray pow-der diffractograms, thermogravimetric analyses, C–H ◊ ◊ ◊ O/N andO–H ◊ ◊ ◊ O/N hydrogen bonds for 1–3. CCDC reference numbers 695986,695987 and 695988 for 1–3, respectively. For ESI and crystallographic datain CIF or other electronic format see DOI: 10.1039/b812670d

donor for building metal–organic networks. The 1,2,4-triazoleligand and its 4-substituted derivatives can be used to obtainlinear coordination polymers based on its bridging function,e.g., with Cu2+,19 Zn2+,20 Cd2+,21 together with a wide variety ofmolecular polynuclear complexes.22 The N1,N2-bridging modeof 1,2,4-triazole or triazolate (Scheme 1) constitutes a shortligand bridge between metal atoms which is a prerequisite forstronger magnetic coupling between paramagnetic metal centers.1

Surprisingly, with the related 4,4¢-bis(1,2,4-triazol-4-yl) ligand(abbreviated as btr) this N1,N2-bridging coordination mode hasonly been observed recently with Cu(II).23 The btr ligand linkstransition metal(II) ions, using only one nitrogen atom from each1,2,4-triazole ring, to one-,24,25 two-, and three-dimensional26–28

networks. With alkylene spacers between the two 1,2,4-triazole

Scheme 1 Ligands relevant to this work. The grey underlined ligands aresynthetically used in this work.

1742 | Dalton Trans., 2009, 1742–1751 This journal is © The Royal Society of Chemistry 2009

rings, the resulting ligand acquires more flexibility. Therefore, weselected 1,2-bis(1,2,4-triazol-4-yl)ethane (abbreviated as btre).29

This btre ligand, which must not be mistaken with the 1,2-bis(1,2,4-triazol-1-yl)ethane ligand,30 has been scarcely used inmetal-complex or MOF synthesis.

A CSD search31 gave 2•{M(NCS)2(m2-btre)2(NCS)2} (M = Fe,

Co)32, 3•{[Cu3(m4-btre)2(m3-btre)4(H2O)2]2(ClO4)12·2H2O}33, 3

•{[Ni3-(m3-btc)2(m4-btre)2(m-H2O)2]·~22H2O}, 3

•{[Ni3(m2-btc)2(m4-btre)2-(m-H2O)2(H2O)2]·4H2O}, 3

•{[Zn3(m4-btc)2(m4-btre)(H2O)2]·2H2O}and 3

•{[Zn3(m6-btc)2(m4-btre)]·~0.67H2O}7 as the only examples.Herein, we report the structures, structure–CPMAS-NMR cor-

relation and luminescence of mixed-ligand coordination networksof bdc2- or ip2- and btre with zinc and cadmium.

Results and discussion

Synthesis

Hydrothermal treatments of metal nitrates with 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) and benzene-1,4-dicarboxylic acid(H2bdc) or benzene-1,3-dicarboxylic acid (H2ip) yield the mixed-ligand coordination polymers 1 to 3 (eqn (1)). Complete deproto-nation of H2ip is achieved through the addition of triethylamine(NEt3).

(1)

The dicarboxylate ligands coordinate towards the metal atomsin 1–3 as shown in Scheme 2.

Scheme 2 The four types of coordination modes of the carboxylategroups of bdc and ip ligands in compounds 1–3.

The vibrational modes for carboxylate groups, substitutedbenzene and triazole rings confirm the presence of deprotonatedbdc, ip and btre ligands in compounds 1–3. The absence of bandsat 1730–1690 cm-1 for –COOH is indicative of fully deprotonatedbdc2- and ip2- ligands in 1–3. The extensive hydrogen-bondingnetwork in the crystal structure of 3 (Table S1, Fig. S9 in ESI†)is indicated through the d- and g-vibrational modes between 880and 1350 cm-1.34

Thermal stability

A sample of compound 1 shows the first weight loss in the TGA(Fig. S4 in ESI†) in the temperature range 260–370 ◦C whichcorresponds to the removal of one btre (or bdc) ligand (obs. 25.0,

calcd. 26.3%). A continuing weight loss from 370 to 600 ◦Cmatches with a complete loss of the remaining 2 bdc or btre +bdc ligands (obs. 54.8, calcd. 52.6%). A sample of compound 2shows the first weight loss in the temperature range 80–160 ◦C inthe TGA (Fig. S5 in ESI†) or up to 110 ◦C in the TGA-IR-MSwhich corresponds to the removal of the crystal water molecule(m/z = 17 and 18 in MS, H2O bands in IR; TGA obs. 2.5, TGA-IR-MS obs. 1.8%, calcd. 2.1%). The weight loss seems to continuemainly with the removal of the btre molecules. In the range 350–420 ◦C the TGA-IR shows bands for nitrile, HCN, NH3 and/orhydrazine and CO2 which matches with the TGA-IR of the freebtre ligand. From 400 ◦C on the MS shows m/z = 50, 52, 76,78, 79, 103, 104 which come from typical aromatic fragments(e.g. 104 = [C6H4-CO]+) and are derived from bdc2-. A remaining32.4% (TGA) or 28% (TGA-IR-MS) suggests the formation ofCdO (calcd. 29.9%). A sample of compound 3 shows the firstweight loss in the temperature range 80–150 ◦C (TGA, Fig. S6 inESI†) or 40–170 ◦C (TGA-IR-MS, Fig. S7†) which corresponds tothe removal of the water molecules (m/z = 17 and 18 in MS, H2Obands in IR, TGA obs. 7.6, TGA-IR-MS obs. 9.4%, calcd. 10.4%).The weight loss continues from 250 ◦C on without pronouncedsteps. Between 250–326 ◦C m/z = 44 (CO2) and 52 in MS, CO2

bands in IR. From 326 ◦C on m/z = 50, 52, 76, 78, 79, 103,104, 105 and 106 as typical aromatic fragments (see above and105 = [C6H5-CO]+) coming from the ip2- moiety (Fig. S8). TheTGA-IR shows bands for nitrile, HCN, NH3 and/or hydrazineand CO2 (Fig. S9 in ESI†). The weight loss continues to 600 ◦Cwhere 38.9% (TGA) or 31% (TGA-IR-MS) of the original mass isretained (ZnO calcd 23.4%).

Crystal structure of 3•{[Zn2(l2-bdc)2(l4-btre)]}, 1. The zinc

compound 1 features a dinuclear metal unit with two crystallo-graphically different bdc ligands, each of them with an inversioncenter in the C6 centroid. One bdc ligand bridges between twoZn atoms with an almost bidentate coordination to each Znwhile the other bdc ligand bridges between two Zn atoms witha monodentate coordination to each metal atom. The btre ligandbridges between four Zn atoms and assumes a cis-bent geometry(Fig. 1). The central C–C bond of the btre ligand is bisected by aC2 axis.

The Zn-bdc substructure consists of criss-crossed 1D chains(Fig. 2a) while the Zn-btre substructure can be pictured as out-of-phase sine-wave chains because of the cis-bent btre-ligandgeometry (Fig. 2b). Both substructures combine to a denselypacked 3D framework (Fig. 3).

Crystal structure of 3•{[Cd2(l4-bdc)(l4-btre)2](NO3)2·H2O}, 2.

The cadmium compound 2 features strands of Cd atoms withneighboring Cd atoms bridged by two btre-triazole groups and abdc-carboxylate group. Hence, each Cd atom is seven coordinatedby four nitrogen and three oxygen atoms. Each bdc2- and the trans-bent btre ligand bridge between four cadmium atoms (Fig. 4).The bdc carboxylate group coordinates in a chelating-bridgingm-kO:kO,O¢ mode to the adjacent Cd atoms. Thus, one O atomof each carboxylate group functions as a bridge between two Cdatoms (Fig. 4 and 5a).

The Cd-bdc substructure is a 2D layer (Fig. 5a), while the Cd-btre substructure is a 3D framework (Fig. 5b). The substructurescombine to a 3D framework with channels along c which are filled

This journal is © The Royal Society of Chemistry 2009 Dalton Trans., 2009, 1742–1751 | 1743

Fig. 1 Coordination environment for a dinuclear zinc unit in 1. Selecteddistances (A) and angles (◦): Zn–O1 1.947(1), Zn–O3 1.961(1), Zn–N27

2.033(1), Zn–N1 2.091(1), Zn—O4 2.471(1), O1–Zn–O3 114.50(4),O1–Zn–N27 109.27(3), O3–Zn–N27 127.62(4), O1–Zn–N1 104.21(3),O3–Zn–N1 93.91(4), N27–Zn–N1 102.01(3), O1–Zn–O4 103.09(3),O3–Zn–O4 58.40(3), N27–Zn–O4 85.24(3), N1–Zn–O4 147.44(3). Sym-metry codes in 1: 2 = -1 - x, y, -0.5 - z; 5 = -1 -x, -y, -z; 7 = -1.5 - x,0.5 - y, -1 - z; 7¢ = -2.5 - x, 0.5 - y, -1 - z.

Fig. 2 Packing analysis for 1 by differentiation in individual(a) {Zn-btc}-strands (some semitransparent for clarity) and (b){Zn-btre}-out-of-phase sine-wave chains. The chain in the backgroundin (b) is depicted semitransparent.

by disordered nitrate ions and less than fully occupied crystal watermolecules (both of them not shown for clarity in Fig. 6).

Crystal structure of 2•{[Zn2(l3-ip)2(l2-btre)(H2O)2]·2H2O}, 3.

The zinc compound 3 features a dinuclear metal unit in which

Fig. 3 Packing diagram for the 3D framework in 1.

Fig. 4 Coordination environment in the cadmium strands in 2. Selecteddistances (A) and angles (◦): Cd–N4 2.338(3), Cd–N54 2.344(3), Cd–N24

2.345(3), Cd–N1 2.345(3), Cd–O24 2.357(2), Cd–O1 2.427(2), Cd–O14

2.464(2), N4–Cd–N54 159.72(10), N4–Cd–N24 85.13(10), N54–Cd–N24

94.89(10), N4–Cd–N1 90.58(10), N54–Cd–N1 83.66(10), N24–Cd–N1163.44(10), N4–Cd–O24 83.95(11), N54–Cd–O24 114.44(11), N24–Cd–O24

112.31(11), N1–Cd–O24 83.03(11), N4–Cd–O1 77.70(9), N54–Cd–O182.10(9), N24–Cd–O1 84.78(9), N1–Cd–O1 78.68(9), O24–Cd–O1153.81(9), N4–Cd–O14 121.65(9), N54–Cd–O14 77.97(9), N24–Cd–O14

78.38(9), N1–Cd–O14 117.18(9), O24–Cd–O14 53.58(9), O1–Cd–O14

152.56(7), Cd–O1–Cd4¢ 108.14(8). Symmetry codes in 2: 4 = 0.5 - x, 0.5 +y, 0.5 - z; 4¢ = 0.5 - x, -0.5 + y, 0.5 - z; 7 = 0.5 - x, 0.5 - y, -z.

two inversion symmetry related Zn atoms are bridged by twocarboxylate groups. Each Zn atom is coordinated by three carboxyloxygen atoms, one nitrogen atom from a btre ligand and oneaqua ligand to give a five-fold coordination sphere in-betweentrigonal bipyramidal and square planar (t = 0.54).35 Each ip2-

ligand bridges between three Zn atoms coordinating to each ofthem monodentate with a different O atom. Each btre ligandconnects only two zinc atoms, thereby using only one N atomon each triazolyl ring for metal coordination (different from theother two structures and from the other reported examples).7,33

The btre ligand assumes a trans-bent geometry (Fig. 7).The Zn-bdc substructure consists of double strands along b

(Fig. 8a) while the Zn-btre substructure consists of individual Zn-btre-Zn pairs (Fig. 8b).

The btre ligands bridge the Zn-bdc double strands to a 2Ddouble layer (Fig. 9). Neighboring double layers are connectedthrough hydrogen bonds from the aqua ligands.

In compounds 1-3 C–H ◊ ◊ ◊ O hydrogen bonds36,37 are presentand in 3, with its aqua ligand and crystal water, also classical


Fig. 5 Packing analysis for 2 by differentiation in individual (a){Cd-btc}-nets and (b) {Cd-btre}-frameworks.

Fig. 6 Packing diagram for the 3D framework in 2. Nitrate ions andwater molecules in the channels are not shown for clarity.

O–H ◊ ◊ ◊ O/N hydrogen bonds38 come into play (see Table S1,Fig. S10-S12 ESI†).

Solid-state CPMAS NMR of 1–3. Carbon-13 solid-stateNMR should be able to reflect among other things the symmetryof the organic ligand(s) in diamagnetic coordination networks.39,40

As such, a collection of solid-state NMR spectra for a certain

Fig. 7 Building unit in 3. Selected distances (A) and angles (◦): Zn–O11.981(1), Zn–O31 2.016(1), Zn–N1 2.081(2), Zn–O22 2.145(1), Zn–O52.198(2), O1–Zn–O31 142.84(6), O1–Zn–N1 112.75(5), O31–Zn–N1103.59(5), O1–Zn–O22 90.35(5), O31–Zn–O22 94.99(5), N1–Zn–O22

93.69(5), O1–Zn–O5 85.33(5), O31–Zn–O5 87.59(5), N1–Zn–O5 89.37(6),O22–Zn–O5 175.42(4). Symmetry codes in 3: 1 = -1 + x, 1 + y, z; 1¢ = 1 +x, -1 + y, z; 2 = -x, 1 - y, 1 - z; 2¢ = -x, 1 - y, 2 - z; 2¢¢ = 1 - x, -y, 1 - z.

Fig. 8 Packing analysis for 3 by differentiation in individual(a) {Zn-ip}-double strands and (b) {Zn-btre}-units.

ligand or ligand combination would eventually not only serve as afingerprint but as a tool to predict the network topology, the na-ture and stereochemistry of hitherto structurally uncharacterizedsolid, amorphous or poorly crystalline coordination polymers.41

Also, solid-state NMR can be a structurally informative


Fig. 9 Packing diagram of 3 showing two double layers with one of themsemitransparent for clarity. The water molecules of crystallization in thechannels are not shown for clarity.

technique for materials containing stoichiometric paramagneticCu(I)/Cu(II)/Zn(II) constituents.42 Structural studies in the solidstate by 13C and 15N CPMAS NMR spectroscopy carried out on aseries of 2-aminotroponimine derivatives have allowed to establishthe existence of hydrogen bonding and to determine the most stabletautomer.43 So far, we are not aware of many in-depth solid-stateNMR investigations of coordination networks.

The 13C CPMAS spectrum of 1 in Fig. 10 shows 9 out of11 signals expected for the symmetry-different (unique) carbonatoms. From the peak integrals the bdc:btre ligand ratio is 2:1.

Fig. 10 13C CPMAS NMR spectrum for 1 and schematic drawing of thebuilding unit with the unique ligand parts given in bold atom symbols.Integral of btre CH set to 1. Regions with rotation side bands at 8 (16)kHz = 64 (128) ppm from the signal are covered in the NMR spectrum.Peak positions: 174.4, 173.3, 152.0, 147.4, 137.9, 132.8, 129.3, 125.6 and48.1 ppm.

The 13C CPMAS spectrum of 2 in Fig. 11 shows 3 out of 4signals expected for the 2 unique CH, the ipso- and CO2 atom ofthe bdc ligand. For the two symmetry independent triazol ringsonly one, slightly broadened CH peak is observed for the fourcrystallographically different btre CH positions. This peak consistsof more than one resonance which could not be resolved. This may

Fig. 11 13C CPMAS NMR spectrum for 2 and schematic drawing of thebuilding unit with the unique ligand parts given with bold atom symbols.Integral of btre CH set to 1. Regions with rotation side bands at 8 (16)kHz = 64 (128) ppm from the signal are covered in the NMR spectrum.Peak positions: 172.6, 147.0, 134.5, 129.0 and 45.9 ppm.

also be due to a symmetry (space group) change with temperatureas the NMR is measured at ambient temperature (~30 ◦C), whilethe X-ray data set is collected at low temperature (-70 ◦C). Thepeak integrals agree with the bdc:btre ligand ratio of 1:2.

A closer inspection of the crystal structure of 2 reveals a pseudomirror plane formed by the Cd atoms in the strand and also bythe Cd-bdc layer (Fig. 12, cf. Fig. 6). Such a mirror plane wouldrender the two triazol rings symmetry equivalent. Furthermore,the environment for the two CH atoms in each triazol ring is verysimilar (Fig. 12). Together this explains the near-equivalency ofthe btre CH atoms leading to a broadening but no splitting of thepeak.

Fig. 12 View along the pseudo mirror plane through the Cd atoms andthe Cd-bdc layer in 2 (cf. Fig. 6) to illustrate the near-equivalency of thetwo triazol rings with C1,C2 and C4,C5.

The 13C CPMAS spectrum of 3 in Fig. 13 is similar to thespectrum of 1 in Fig. 10 and shows 9 out of 11 signals expectedfor the symmetry-different (unique) carbon atoms of the ligands.Also, the peak integral of the benzene-dicarboxylate (ip) and btre


Fig. 13 13C CPMAS NMR spectrum for 3 and schematic drawing of thebuilding unit with the unique ligand parts given with bold atom symbols.Integral of btre CH set to 1. Regions with rotation side bands at 8 (16)kHz = 64 (128) ppm from the signal are covered in the NMR spectrum.Peak positions: 176.7, 174.6, 147.1, 143.7, 136.3, 133.3, 131.5, 129.7 and46.7 ppm.

signals is as seen in 1 (Fig. 10) and agrees with the ip:btre ligandratio of 2:1.

Luminescence properties of 1–3. The d10 zinc and cadmiummixed-bdc/ip-btre-ligand coordination polymers 1-3 show strongfluorescence emissions at 445 (1), 421 (2) and 423 nm (3) uponexcitation at 335 (1), 328 (2) and 320 nm (3) (Fig. 14). The free1,2-bis(1,2,4-triazol-4-yl)ethane ligand (btre) gives no fluorescenceresponse at room temperature. A possible btre fluorescencethrough an intra-ligand charge transfer is apparently quenchedby the thermal intra-ligand rotations around the C–C and C–Nbonds.

Conclusions

The ligand combination of 1,2-bis(1,2,4-triazol-4-yl)ethane (btre)and fully deprotonated benzene-1,3- or -1,4-dicarboxylate (ip2-

or bdc2-) with zinc and cadmium cations leads to 3D (withbdc2-) or 2D (with ip2-) metal–organic frameworks. The bdc/ipto btre ligand ratio and the ligand local site symmetry is reflectedin the solid-state CPMAS 13C NMR spectra. Zinc or cadmiumcoordination to benzenedicarboxylate and the btre ligand gives astrong luminescence response upon UV excitation (the free btreligand is non-luminescent). Further studies on the luminescentproperties of metal-btre compounds are in progress.

Experimental

Commercially available solvents, monoformylhydrazine, triethylorthoformate, ethylenediamine, benzene-1,4-dicarboxylic acid

Fig. 14 Excitation (Exc) and emission (Em) spectra of compounds 1–3;the respective excitation (emission spectra) and monitoring (excitationspectra) wavelengths are given.

(H2bdc), benzene-1,3-dicarboxylic acid (H2ip), triethylamine,Zn(NO3)2·4H2O and Cd(NO3)2·4H2O were used without furtherpurification. The ligand 1,2-bis(1,2,4-triazol-4-yl)ethane (btre)was prepared according to the method from Bayer.44 Driedmethanol is used for the preparation of the btre ligand. Elementalanalyses were performed on a VarioEL from Elementaranalysen-systeme GmbH. Infrared spectra were recorded in the range 400–4000 cm-1 on a Bruker Optik IFS 25 spectrophotometer usingKBr pellets. Thermogravimetric analysis was carried out in asimultaneous thermoanalysis apparatus STA 409C from Netzschunder nitrogen with a heating rate of 10 ◦C min-1 in the range50 to 600 ◦C. The filled sample container was conditioned byfirst applying oil pump vacuum down to 1 bar for 5 min, thenflushing with nitrogen. TGA-IR and TGA-MS were recordedsimultaneously on the Mettler TGA/SDTA 851e coupled withthe Nicolet Nexus 470 gas phase FTIR and the Balzers (PfeifferVacuum) Quadrupole MS. Experiments were done under Argon


(60 ml/min) in 900 ml alox crucibles between 30 and 600◦Cwith 10◦C/min. Powder X-ray diffraction patterns were measuredat ambient temperature using a STOE STADI-P with Debye-Scherrer geometry, Mo-Ka radiation (l = 0.7093 A), a Ge(111)monochromator and the samples in glass capillaries on a rotatingprobe head. Simulated powder patterns were based on single-crystal data and calculated using the STOE WinXPOW softwarepackage.45

Syntheses

catena-[(l2 -Benzene-1,4-dicarboxylato-j2O,O¢:j2O¢¢,O¢¢¢)-(l2 -benzene-1,4-dicarboxylato-jO:jO¢¢)-(l4 -1,2-bis(1,2,4-triazol-4-yl)ethane-jN1:jN1¢:jN2:jN2¢)-dizinc(II)], 3

•{[Zn2(l2-bdc)2(l4-btre)]} (1). A mixture of Zn(NO3)2·4H2O (131 mg, 0.50 mmol),H2bdc (83 mg, 0.50 mmol), btre (82 mg, 0.50 mmol) and water(15 mL) was stirred for 30 min. at room temperature and the pHvalue of the final mixture was adjusted to 6.50 by addition oftriethylamine, then the mixture is transferred to a Teflon-linedstainless-steel autoclave and heated at 160 ◦C for 3 d, then it wascooled to room temperature at a rate of 10 ◦C h-1. A colorlesscrystalline product, which was suitable for X-ray single crystalanalysis, was filtered off, washed with distilled water and driedin air (Yield 96 mg, 62% based on Zn). Elemental analysisC22H16Zn2N6O8 (623.18) calcd. C 42.40, H 2.59, N 13.49; found:C 42.80, H 2.74, N 13.06%; IR (KBr) 3102(w), 3050(w), 3008(w),1602(s, nasymCO2), 1570(m, nasymCO2), 1503(m), 1445(m, nsymCO2),1395(m, nsymCO2), 1342(m), 1204(m), 1169(m), 1141(m), 1078(s),1046(s), 1013(s), 940(w), 915(w), 888(m), 842(s), 812(s), 750(s),648(s), 586(s), 514(m), 471(w) cm-1.

catena-[(l4 -Benzene-1,4-dicarboxylato-jO:j2O,O¢:jO¢¢:j2O¢¢,O¢¢¢)-bis(l4-1,2-bis(1,2,4-triazol-4-yl)ethane-jN1:jN1¢:jN2:jN2¢)-dicadmium(II)] dinitrate hydrate, 3

•{[Cd2(l4-bdc)(l4-btre)2](NO3)2·H2O} (2). A mixture of Cd(NO3)2·4H2O (154 mg, 0.50 mmol),H2bdc (83mg, 0.50 mmol), btre (82 mg, 0.50 mmol) and water(15 mL) was stirred for 30 min. at room temperature and the pHvalue of the final mixture was adjusted to 5.00 by addition oftriethylamine, then the mixture is transferred to a Teflon-linedstainless-steel autoclave and heated at 160 ◦C for 3 d, then it wascooled to room temperature at a rate of 10 ◦C h-1. A colorlesscrystalline product, which was suitable for X-ray single crystalanalysis, was filtered off, washed with distilled water and driedin air (Yield 115 mg, 54% based on Cd). Elemental analysisC20H22Cd2N14O11 (859.32) calcd. C 27.96, H 2.58, N 22.82;found: C 27.61, H 2.26, N 22.67%; IR (KBr) 3442(w, n(O-H)),3110(w), 1656(m, nasymCO2), 1553(s, nasymCO2), 1504(s), 1434(m,nsymCO2), 1378(s, nsymCO2), 1342(w), 1286(w), 1202(s), 1160(m),1112(w), 1079(s), 1032(m), 1016(m), 993(m), 884(m), 844(s),746(s), 684(m), 640(s), 526(s), 488(w) 457(w), 407(w) cm-1.

catena-[Diaqua-bis(l3-benzene-1,3-dicarboxylato-jO:jO¢:jO¢¢)-(l2-1,2-bis(1,2,4-triazol-4-yl)ethane-jN1:jN1¢)dizinc(II)] dihyd-rate, 2

•{[Zn2(l3-ip)2(l2-btre)(H2O)2]·2H2O} (3). A mixture ofZn(NO3)2·4H2O (131 mg, 0.50 mmol), H2ip (83mg, 0.50 mmol),triethylamine (140 mL, 1.50 mmol), btre (82 mg, 0.50 mmol)and water (15 mL) was stirred for 30 min. at room temperature,then the mixture is transferred to a Teflon-lined stainless-steelautoclave and heated at 180 ◦C for 3 d, then it was cooled toroom temperature at a rate of 2.8 ◦C h-1. A colorless crystalline

product, which was suitable for X-ray single crystal analysis wasfiltered off, washed with distilled water and dried in air (Yield120 mg, 69% based on Zn). Elemental analysis C22H24Zn2N6O12

(695.26) calcd. C 38.01, H 3.48, N 12.09; found: C 38.02, H 3.75,N 12.32%; IR (KBr) 3566 and 3497(w, n(O-H)), 3122(w), 1609(s,nasymCO2), 1562(s, nasymCO2), 1479(m), 1429(s, nsymCO2), 1371(s,nsymCO2), 1273(w), 1195(m, d(OH ◊ ◊ ◊ O)), 1174(w), 1078(m),1018(m), 981(w), 900(m, g(OH ◊ ◊ ◊ O)), 824(m), 800(w), 752(s),720(s), 686(m), 640(s), 576(m), 463(w), 434(w), 408(w) cm-1.

X-Ray crystallography†

Suitable single crystals were carefully selected under a polarizingmicroscope. Data collection: Bruker AXS with APEX2 CCD area-detector, temperature 203(2) K, Mo-Ka radiation (l = 0.71073A), graphite monochromator, double-pass method w-scan. Datacollection with APEX2, cell refinement and data reduction withSAINT,46 experimental absorption correction with SADABS.47

Structure analysis and refinement: The structure was solved bydirect methods (SHELXS-97); refinement was done by full-matrixleast squares on F 2 using the SHELXL-97 program suite.48 Allnon-hydrogen positions refined with anisotropic displacementparameters. Hydrogen atoms were positioned geometrically (aro-matic C–H = 0.94 A, 0.98 A for CH2) and refined using ariding model (AFIX 43 for aromatic CH, AFIX 23 for CH2)with Uiso(H) = 1.2 Ueq(CH, CH2). In 2 the nitrate ions aredisordered over at least two positions. Their N and O atoms couldonly be refined isotropically. The crystal water molecule in 2 isdisordered over two positions with about 0.25 occupancy, each.Only the oxygen atoms could be found and refined isotropically.In 3 hydrogen atoms on the aqua ligands and the crystal waterwere found and refined with Uiso(H) = 1.5Ueq(O). Simulated X-raypowder diffractograms from the single-crystal data were matchedwith measured X-ray powder diffractograms for 1, 2 and 3 toverify the representative nature of the single crystal with respect tothe bulk material (Fig. S1-S3 ESI).† Graphics were obtained withDIAMOND.49 Crystal data and details on the structure refinementare given in Table 1.

Luminescence measurements

Photoluminescence analyses for compounds 1, 2 and 3 wereperformed using powdered samples at room temperature indiffuse reflection geometry on a Perkin Elmer LS55 fluorescencespectrometer equipped with a Xe discharge lamp (equivalent to20 kW for 8 ms duration) and a gated photomultiplier withmodified S5 response. The acquisition time was 100 nm/min.

CPMAS NMR

All spectra were recorded using 2.5 mm rotors on a Bruker Avance500 solid-state NMR spectrometer (11.7 T) operating at Lamorfrequencies of 125.78 MMz for 13C. RF pulses were applied ata transverse B1 field of 125 kHz corresponding to a p/2 pulsewidth of 2 ms. 13C {1H} CPMAS experiments were performedunder magic angle spinning at 8 KHz with bearing gas at ambienttemperature. Cross polarization was achieved using a ramp50 withtypically 1024 steps applied to the proton channel ranging from 80to 100% and a contact time of 2 ms. In all 13C experiments, TPPM


Table 1 Crystal data and structure refinement for 1 to 3

Compound 1 2 3

Empirical formula C11H8ZnN3O4e C10H11CdN7O5.5

ef C11H12ZnN3O6e

M/g mol-1 311.59e 429.66ef 347.63e

Crystal size/mm 0.60 ¥ 0.25 ¥ 0.20 0.32 ¥ 0.12 ¥ 0.02 0.25 ¥ 0.09 ¥ 0.012q range/◦ 4.6–77.2 3.9–51.7 6.1–71.0Completeness to 2q/% 100g 99.8 96.8g

h; k; l range ±22; -26, +25; -22, +23 ±28; ±9; ±23 -12, +9; -15, +9; -13, +16Crystal system Monoclinic Monoclinic TriclinicSpace group C2/c C2/c P-1a/A 12.455(1) 22.9206(8) 7.4247(2)b/A 15.158(1) 7.7047(2) 9.3631(2)c/A 13.274(2) 19.3208(7) 10.1580(2)a/◦ 90.00 90 81.657(1)b/◦ 117.43(1) 114.596(3) 70.675(1)g /◦ 90.00 90 71.704(1)V/A3 2224.3(4) 3102.4(2) 632.02(3)Z 8 8 2Dcalc/g cm-3 1.861 1.840f 1.827F (000) 1256 1696f 354m/mm-1 2.223 1.449f 1.977Max/min transmiss. 0.6382/0.3349 0.9716/0.6543 0.9805/0.6378Refl. collected (Rint) 46785 (0.0288) 20459 (0.0395) 8293 (0.0192)Indep. reflections 6281 3001 4087Obs. refl. [I > 2s(I)] 5188 2633 3464Parameters refined 172 216 202Max./min. Dr/e A-3a 0.614/-0.294 1.581/-0.589 0.472/-0.335R1/wR2 [I >2s(I)]b 0.0263/0.0676 0.0285/0.0745 0.0304/0.0702R1/wR2 (all reflect.)b 0.0376/0.0719 0.0334/0.0774 0.0394/0.0741Goodness-of-fit on F 2c 1.024 1.053 1.038Weight. scheme w; a/bd 0.0397/0.7942 0.0438/10.1578 0.0350/0.2008

a Largest difference peak and hole. b R1 = [∑

(‖F o| - |F c‖)/∑

|F o|]; wR2 = [∑

[w(F o2 - F c

2)2]/∑

[w(F o2)2]]1/2. c Goodness-of-fit = [

∑[w(F o

2 - F c2)2]/(n -

p)]1/2. d w = 1/[s 2(F o2) + (aP)2 + bP] where P = (max(F o

2 or 0) + 2F c2)/3. e Throughout the text the doubled formula of the asymmetric unit was used to

have full ligand numbers. f H atoms on crystal water not located but included in formula, formula mass, density, F (000) and m calculation. g Completenessto 2q = 50◦.

dipolar decoupling51 was employed. 13C spectra were referenced tothe methyne resonance of alanine (51 ppm).

Acknowledgements

The work is supported by KAAD and DFG grant Ja466/14-1. Wethank Dr Pierre Fux and the Research Analytics Department ofCiba Inc., Basel, Switzerland for the TG-IR-MS experiments.

Notes and references

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crystal structures and solid-state cpmas 13c nmr correlations in luminescent zinc(ii) and...

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